(1) Field of the Invention
The present invention relates to a locking unit, and more particularly, a locking unit for a seat belt retractor which is provided on one end of a spool around which a seat belt is wound, and which is constructed such that, when the seat belt is rapidly unwound, for example, when a vehicle collision occurs, a locking part of the locking arm, a rotating center of which is disposed away from the center axis of the spool, is locked to an internal gear, thus locking the seat belt.
(2) Description of the Related Art
Generally, as seat belt systems for vehicles, three-point seat belt systems, in which first and second portions of a seat belt are respectively coupled to upper and lower ends of a pillar panel in a passenger compartment, and which are constructed such that a passenger pulls a third portion of the seat belt and fastens it to a predetermined portion of the seat, have been widely used. In such a three-point seat belt system, a spool is provided in the upper end of the pillar panel, and a retractor is provided to make it possible to wind the seat belt on the spool. Furthermore, a height adjustment unit for adjusting the height of the spool is provided in the seat belt system, so that the passenger can adjust the height of the spool to correspond to his/her sitting height.
Meanwhile, when a vehicle collision occurs, the passenger leans forwards due to inertia. At this time, to protect the upper body of the passenger, the seat belt must instantaneously lock in response to the collision. As well as in the event of such a collision, this function must also be conducted when the vehicle stops suddenly. To achieve the above-mentioned purpose, a locking unit of a retractor is provided in the spool of the vehicle seat belt system. The locking unit serves as a safety device for holding the spool such that, when the seat belt is rapidly unwound, the spool is prevented from rotating.
A conventional seat belt 1 and a locking unit therefore will be explained with reference to FIGS. 1 and 2. In the seat belt 1, which is a three-point type, a spool 10 is provided in the upper end of a pillar panel. The height of the spool 10 is adjusted by pushing and moving a height adjustment unit 3 upwards or downwards such that a member 5, in which the spool is installed, is moved upwards or downwards.
A locking unit of a retractor is provided on one end of the spool 10. The locking unit has an external gear 19 on the circumferential outer surface thereof Furthermore, a locking arm 30 is provided on a shaft 32, which is disposed away from the rotating center 70 of the spool 10 in a predetermined distance. A protrusion type locking part is provided on a first end of the locking arm 30. A front stopper 12 and a rear stopper 14 are provided to define the range within which the locking part can move, wherein the protrusion type locking part is disposed between the front stopper 12 and the rear stopper 14. A second end of the locking arm 30 is supported by a spring 18 and is stopped at a predetermined position by another stopper 16. In addition, an inertia actuating member 50 is provided adjacent to the second end of the locking arm 30 to prevent the locking arm 30 from rotating when the belt is rapidly unwound. An internal gear 92, to which the protrusion type locking part of the locking arm 30 is locked by inertia, is provided in the locking unit. The internal gear 92 is fixed to a housing 90, so that, when the belt is wound or unwound, the spool 10 is rotated inside the housing 90, but the internal gear 92 maintains the stationary state.
FI. 2A is a view showing the locking unit under normal conditions. FIG. 2B is a view showing the locking unit when it is in a locked state. As shown in the drawings, when the belt 1 is unwound, the spool 10 is rotated in a counterclockwise direction. At this time, the locking part of the locking arm 30 is not locked to the internal gear 92. The spool 10 is rotated in the housing 90. Meanwhile, when the belt 1 is rapidly unwound, the spool 10 is rapidly rotated in a counterclockwise direction. Simultaneously, the locking arm 30 is rotated in a clockwise direction by inertia, so that the locking part of the locking arm 30 is locked to the internal gear 92. At this time, the front stopper 12 attached on the spool 10 stops the rotation of the locking arm 30. Thus, the spool 10 can no longer rotate. Using this method, when the vehicle stops suddenly or is in a collision, the spool 10 is locked and is prevented from rotating, thus preventing the belt 1 from being unwound, thereby protecting the passenger.
However, in the case of the conventional locking unit for the seat belt retractor, the locking arm is rotated by inertia not only when the belt is rapidly unwound but also when the belt is rapidly wound, in which case the belt is undesirably locked. This is called an end lock phenomenon. The end lock phenomenon occurs when the belt is wound or the height adjustment unit is rapidly moved downwards. In detail, when the belt is wound, the retractor rapidly winds the belt around the spool. When the retraction of the belt is completed, that is, when the spool, which has been rotated, is stopped, the locking arm is rotated by inertia and is thus locked to the internal gear. In the case where the height adjustment unit is rapidly moved downwards, the belt is wound by the retractor to a length corresponding to the distance that the spool is moved downwards. At this time, the above-mentioned end lock phenomenon occurs. As such, the conventional locking unit for the retractor is a safety device to ensure readiness for the case where the belt is rapidly unwound, but there is a problem in that the belt is also locked when the belt is rapidly wound, which is undesirable in that it inconveniences the user and parts thereof may be damaged.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.